Method and system to regulate cooling of a medical imaging device

ABSTRACT

The present invention provides a system and method of removing heat from an MR imaging device while maintaining internal and external temperatures below maximum operating limits, thereby enabling higher power applications for faster imaging with improved image quality as well as, allowing longer scan times for interventional procedures. The system includes a vacuum chamber housing the gradient coils and a vacuum pump connected thereto to regulate the pressure and humidity within the chamber. A heat exchanger, coolant pump, and controller are provided to regulate the temperature of coolant designed to dissipate heat from the gradient coils in response to at least one temperature sensor.

BACKGROUND OF INVENTION

[0001] The present invention relates generally to magnetic resonanceimaging (MRI) apparatus, and more particularly to, a system and methodto provide improved cooling to an MRI apparatus and thereby enablehigher power applications for faster imaging with improved image qualityand allow longer scan times.

[0002] When a substance such as human tissue is subjected to a uniformmagnetic field (polarizing field B₀), the individual magnetic moments ofthe spins in the tissue attempt to align with this polarizing field, butprecess about it in random order at their characteristic Larmorfrequency. If the substance, or tissue, is subjected to a magnetic field(excitation field B₁) which is in the x-y plane and which is near theLarmor frequency, the net aligned moment, or “longitudinalmagnetization”, M_(Z), may be rotated, or “tipped”, into the x-y planeto produce a net transverse magnetic moment M_(t). A signal is emittedby the excited spins after the excitation signal B₁ is terminated andthis signal may be received and processed to form an image.

[0003] When utilizing these signals to produce images, magnetic fieldgradients (G_(x)G_(y) and G_(z)) are employed. Typically, the region tobe imaged is scanned by a sequence of measurement cycles in which thesegradients vary according to the particular localization method beingused. The resulting set of received NMR signals are digitized andprocessed to reconstruct the image using one of many well knownreconstruction techniques.

[0004] During patient scans, the gradient coils that produce themagnetic field gradients dissipate large amounts of heat, typically onthe order of tens of kilowatts. The majority of this heat is generatedby resistive heating of the copper electrical conductors that form thex, y, and z-axis gradient coils when these coils are energized. Theamount of heat generated is in direct proportion to the electrical powersupplied to the gradient coils. The large power dissipations not onlyresult in increased temperature to the gradient coil, the heat producedis distributed within the gradient coil assembly, or resonance modules,and influences the temperature in two other critical regions. These tworegions are located at the boundaries of the gradient assembly andinclude the patient bore surface and the warm bore surface adjacent tothe cryostat that houses the magnets. Each of these three regions hasspecific maximum temperature limitations. In the resonance module, thereare material temperature limitations, such as the glass transitiontemperature. That is, although the copper and fiber-reinforced backingof the coils can tolerate temperatures in excess of 120° C., the epoxyto bond the layers typically has a much lower maximum workingtemperature of approximately 70-100° C. On the patient bore surface,regulatory limits mandate a peak temperature on the patient bore surfaceof 41° C. The warm bore surface also has a maximum temperature that islimited to approximately 40° C. to prevent excessive heat transferencethrough the warm bore surface and into the cryostat. Further,temperature changes of more than 20° C. can cause field homogeneityvariations due to a temperature dependence of the field shim materialthat exhibits a magnetic property variation with temperature.

[0005] Typically, the heat produced by the gradient coils in theresonance modules is removed from the gradient assembly by liquid filledcooling tubes embedded in the resonance modules at a given distance fromthe heat conductors. A liquid coolant, such as water, ethylene, or apropylene glycol mixture, enters the resonance module at a fixedtemperature and flow rate, absorbs heat from the gradient coils as it ispumped through the cooling tubes, and transports the heat to a remoteheat exchanger/water chiller. Heat is then ejected to the atmosphere byway of the heat exchanger/chiller. For each degree reduction of thecoolant temperature as it enters the resonance module, the peaktemperatures at each of the three critical regions (resonance moduleinterior, patient bore surface, and warm bore surface) are also lowered.

[0006] However, in current systems, the minimum temperature of thecoolant supplied to the resonance modules is limited by the dew pointtemperature of the ambient air. That is, since it is necessary toprevent the water vapor in the air from condensing in the resonancemodules in general, and on the gradient coils in particular, thetemperature of the coolant must remain above the dew point temperatureof the ambient air. The high voltages and currents that are applied tothe gradient coils dictates an atmosphere that must be free of suchcondensation. Current environmental specifications for MR rooms require75% relative humidity at 21° C., which requires a dew point temperatureof 16° C. Therefore, the minimum coolant temperature must be above 16°C. under these conditions.

[0007] The maximum power which can be supplied to a resonance module istherefore limited by the external dew point temperature. To increase thepower which can be received by the resonance module, it is necessary tolower the minimum coolant temperature. However, as indicated previously,environmental specifications limit the minimum coolant temperature toabove 16° C. for an MR room with 75% relative humidity at 21° C. As aresult, these current systems are unable to accommodate higher powerpatient scan sequences often required by resonance modules.

[0008] In these known systems, the lowest permissible coolanttemperature is dictated by atmospheric conditions or the ambient dewpoint temperature. With these systems, the coolant temperature is setabove the worst case dew point temperature based upon the giventemperature and relative humidity specifications in the room housing theMR system.

[0009] Further, these systems must be kept from overheating. In case ofincreased temperatures of the resonance module or the patient surface,imaging scans must be interrupted or limited to low power sequences,which in turn reduces the efficiency and efficacy of the MR system. Timeis then lost because imaging sessions cannot begin anew until theresonance module or patient surface cools sufficiently.

[0010] It would therefore be desirable to design a method and system todissipate more heat during imaging scans independent of theaforementioned minimum coolant temperature limitation dictated by thedew point temperature of the ambient air.

SUMMARY OF INVENTION

[0011] The present invention provides a system and method overcoming theaforementioned drawbacks by removing heat with lower coolanttemperatures in a vacuum chamber containing the gradient and RF coils ofan imaging device while maintaining internal and external temperaturesbelow maximum operating limits, thereby enabling higher powerapplications for faster imaging with improved image quality, as well as,allowing longer scan times for interventional procedures.

[0012] A cooling system is provided with improved heat dissipation foran MRI resonance device. The cooling system includes a vacuum enclosure,a set of relative humidity, temperature and pressure sensors, and acontrol system that dynamically adjusts the temperature of coolant incooling tubes embedded in the resonance module. The cooling fluidincreases in temperature as it absorbs heat from the resonance moduleand transports the heat to a remote heat exchanger, such as, a waterchiller. Since air and water vapor are removed from the vacuum enclosurecontaining the resonance module, condensation is prevented in theevacuated enclosure. As a result, the coolant temperature may beadjusted as needed to remove heat and maintain gradient coiltemperatures within allowable levels.

[0013] Moreover, to further enhance proper operation and reliability,pressure and relative humidity sensors are placed in the vacuumenclosure to monitor for air and/or coolant leakage. To preventcondensation of water vapor on the exterior surfaces of the gradientcoil, temperature sensors are installed on the patient and warm boresurfaces and in the vacuum enclosure. The control system is configuredto provide the lowest practical coolant temperature while simultaneouslypreventing condensation on the patient and warm bore surfaces.Additionally, the relative humidity and pressure sensors may be used totrigger an alarm and disable the gradient coil drivers in response to ananomalous operating condition.

[0014] In accordance with one aspect of the present invention, a systemfor cooling electrical coils is provided. The system includes a coilingtube assembly for transferring heat from at least one electrical coilvia a coolant traveling through the coil assembly and a heat exchangerfor receiving the coolant from the cooling tube assembly. The heatexchanger is configured to remove heat from the coolant received fromthe cooling tube assembly. An enclosure is also provided and includesthe cooling tube assembly therein. The enclosure is designed to have aninternal dew point less than that of a surrounding atmosphere. A controlsystem receives feedback indicative of operating conditions of theelectrical coil and in response thereto, provides control signals to achiller in order to dynamically adjust coolant temperatures.

[0015] In a further aspect of the present invention, a cooling systemfor an MRI device includes a set of coolant tubes in thermal contactwith a set of gradient coils of the MR device and having a coolant passtherethrough. A heat exchanger is connected to the set of coolant tubesand configured to remove heat entrained in the coolant. A vacuum chamberencloses the set of coolant tubes. At least one temperature sensor isprovided that is in a thermal contact to sense temperature of the MRdevice and a humidity sensor is positioned to sense humidity in thevacuum chamber. The system includes a controller connected to receivetemperature indicative signals from the temperature sensor and controlcoolant temperature in response thereto.

[0016] In yet another aspect of the present invention, an MRI apparatusis provided and includes a magnetic resonance imaging (MRI) systemhaving a plurality of gradient coils. The gradient coils are configuredto be positioned about a bore of a magnet to impress a polarizingmagnetic field. The MRI system further includes an RF transceiver systemand an RF switch controlled by a pulse module to transmit RF signals toan RF coil assembly to acquire MR images. The MRI apparatus alsoincludes a cooling system to dissipate heat from the plurality ofgradient coils. The cooling system includes a temperature sensorpositioned to sense gradient coil temperature and a set of coolant tubeshaving a coolant pass therethrough and in thermal contact with thegradient coils of the MR system. A heat exchanger is connected to thecoolant tubes to remove heat from the coolant wherein the coolant tubesare enclosed by a vacuum chamber. A vacuum pump connected to the vacuumchamber is provided to maintain a vacuum within the chamber. The MRIapparatus also includes at least one pressure sensor configured to sensepressure within the vacuum chamber. A control is connected to receivesignals from the pressure sensor and to send control signals to thevacuum pump. The control is also connected to receive signals from thetemperature sensor to control a coolant temperature in response. In thismanner, the system is able to maintain a steady gradient coiltemperature by varying the coolant temperature.

[0017] In yet a further aspect of the present invention, a method ofcooling an MRI device is also provided. The method includes the steps ofcreating a sealed enclosure about a set of gradient coils and removingmoisture from the sealed enclosure. The method also includes the step ofrecirculating a coolant through a series of cooling tubes in the sealedenclosure and through a heat exchanger. Next, an indication of gradientcoil temperature is monitored during MR operation and the temperature ofthe coolant is adjusted in response to the indication of gradient coiltemperature.

[0018] Various other features, objects and advantages of the presentinvention will be made apparent from the following detailed descriptionand the drawings.

BRIEF DESCRIPTION OF DRAWINGS

[0019] The drawings illustrate one preferred embodiment presentlycontemplated for carrying out the invention. In the drawings:

[0020]FIG. 1 is a schematic block diagram of an MRI imaging system foruse with the present invention.

[0021]FIG. 2 is a schematic drawing of a cooling system for use with theMRI imaging system shown in FIG. 1.

[0022]FIG. 3 is a flow chart illustrating the steps of a thermal controltechnique for use with the present invention.

DETAILED DESCRIPTION

[0023] Referring to FIG. 1, the major components of a preferred magneticresonance imaging (MRI) system 10 incorporating the present inventionare shown. The operation of the system is controlled from an operatorconsole 12 which includes a keyboard or other input device 13, a controlpanel 14, and a display 16. The console 12 communicates through a link18 with a separate computer system 20 that enables an operator tocontrol the production and display of images on the screen 16. Thecomputer system 20 includes a number of modules which communicate witheach other through a backplane 20 a. These include an image processormodule 22, a CPU module 24 and a memory module 26, known in the art as aframe buffer for storing image data arrays. The computer system 20 islinked to disk storage 28 and tape drive 30 for storage of image dataand programs, and communicates with a separate system control 32 througha high speed serial link 34. The input device 13 can include a mouse,joystick, keyboard, track ball, touch activated screen, light wand,voice control, or any similar or equivalent input device, and may beused for interactive geometry prescription.

[0024] The system control 32 includes a set of modules connectedtogether by a backplane 32 a. These include a CPU module 36 and a pulsegenerator module 38 which connects to the operator console 12 through aserial link 40. It is through link 40 that the system control 32receives commands from the operator to indicate the scan sequence thatis to be performed. The pulse generator module 38 operates the systemcomponents to carry out the desired scan sequence and produces datawhich indicates the timing, strength and shape of the RF pulsesproduced, and the timing and length of the data acquisition window. Thepulse generator module 38 connects to a set of gradient amplifiers 42,to indicate the timing and shape of the gradient pulses that areproduced during the scan. The pulse generator module 38 can also receivepatient data from a physiological acquisition controller 44 thatreceives signals from a number of different sensors connected to thepatient, such as ECG signals from electrodes attached to the patient.And finally, the pulse generator module 38 connects to a scan roominterface circuit 46 which receives signals from various sensorsassociated with the condition of the patient and the magnet system. Itis also through the scan room interface circuit 46 that a patientpositioning system 48 receives commands to move the patient to thedesired position for the scan.

[0025] The gradient waveforms produced by the pulse generator module 38are applied to the gradient amplifier system 42 having G_(x), G_(y), andG_(z) amplifiers. Each gradient amplifier excites a correspondingphysical gradient coil in a gradient coil assembly generally designated50 to produce the magnetic field gradients used for spatially encodingacquired signals. The gradient coil assembly 50 forms part of a magnetassembly 52 which includes a polarizing magnet 54 and a whole-body RFcoil 56. A transceiver module 58 in the system control 32 producespulses which are amplified by an RF amplifier 60 and coupled to the RFcoil 56 by a transmit/receive switch 62. The resulting signals emittedby the excited nuclei in the patient may be sensed by the same RF coil56 and coupled through the transmit/receive switch 62 to a preamplifier64. The amplified MR signals are demodulated, filtered, and digitized inthe receiver section of the transceiver 58. The transmit/receive switch62 is controlled by a signal from the pulse generator module 38 toelectrically connect the RF amplifier 60 to the coil 56 during thetransmit mode and to connect the preamplifier 64 to the coil 56 duringthe receive mode. The transmit/receive switch 62 can also enable aseparate RF coil (for example, a surface coil) to be used in either thetransmit or receive mode.

[0026] The MR signals picked up by the RF coil 56 are digitized by thetransceiver module 58 and transferred to a memory module 66 in thesystem control 32. A scan is complete when an array of raw k-space datahas been acquired in the memory module 66. This raw k-space data isrearranged into separate k-space data arrays for each image to bereconstructed, and each of these is input to an array processor 68 whichoperates to Fourier transform the data into an array of image data. Thisimage data is conveyed through the serial link 34 to the computer system20 where it is stored in memory, such as disk storage 28. In response tocommands received from the operator console 12, this image data may bearchived in long term storage, such as on the tape drive 30, or it maybe further processed by the image processor 22 and conveyed to theoperator console 12 and presented on the display 16.

[0027] The present invention provides a system and method to improveheat removal from the gradient coil housing, or resonance module, of animaging device while maintaining internal and external temperaturesbelow maximum operating limits, thereby enabling higher powerapplications for faster imaging with improved image quality as well as,allowing longer scan times for interventional procedures.

[0028] Referring to FIG. 2, a cooling system 70 is provided andconfigured to reduce heat generated by the gradient coils of a magneticresonance imaging (MRI) system 10. Dissipating heat generated within anMRI device 10 is paramount to avoid overheating and potential damage tothe gradient coils. The MRI device 10 includes a cryogenic tank 71 tohouse the main magnet (not shown) and an imaging volume space 72 for asubject, such as, a medical patient, to be placed to undergo an imagingsession. The imaging volume is defined by a vacuum pumped enclosure, orresonance module, 74 configured to house the gradient coils and the RFcoils. As indicated previously, the gradient coils are excited by acorresponding gradient amplifier to produce magnetic field gradientsused for spatially encoding signals acquired by the RF coils used toreconstruct an image in a known manner.

[0029] Further enclosed in vacuum chamber 74 are a number of coolingtubes 76 configured to circulate liquid coolant, such as water,ethylene, or a propylene glycol mixture, to reduce heat generated by theexcitation of the gradient coils. When generating the magnetic fieldgradients, the gradient coils, as a result of the resistive effects oftheir copper composition, generate considerable heat, typically on theorder of tens of kilowatts, which must be dissipated to ensure properoperation of the MRI system 10. To assist in heat dissipation, coolantis circulated through the cooling tubes 76 embedded in resonance module74, as will be discussed shortly.

[0030] As indicated previously, resonance module 74 is maintained in avacuous state. Enclosing resonance module 74 in a vacuum operates toexpunge any air and water vapor accumulating in the resonance module. Asis well known, circulating a liquid having a temperature less than thetemperature of the surrounding environment may result in condensationforming in the resulting environment. That is, circulating coolantthrough tubes 76 to dissipate heat from the gradient coils in anon-vacuous chamber could result in condensation forming on the surfaceof the gradient coils if the coolant temperature is below the dew pointin the chamber. Since condensation cannot be allowed to form on thesurface of the gradient coils, preexisting cooling systems havemaintained the temperature of the coolant above the dew point.

[0031] Maintaining a vacuous state within the enclosed vacuum chamber 74eliminates the possibility of condensation on the gradient coils of theMR apparatus. The present invention provides a vacuum pump 78 in flowcommunication with each vacuum chamber 74. The vacuum pump is configuredto frequently expunge any air and/or moisture in the vacuum chamber 74by maintaining a vacuum condition of approximately 10⁻¹ to 10² torr.Vacuum pump 78 is controlled by a control system, such as a computer orcontroller 80 that is configured to control the operation of the vacuumpump 78. That is, computer/controller 80 may signal the vacuum pump todecrease or increase the pressure within the enclosure 74. Stillreferring to FIG. 2 and as indicated previously, condensation may formon the surface of the gradient coils in response to the circulation ofcoolant that is below the ambient dew point if not for a consistentvacuous state within chamber 74. Coolant enters the resonance module orchamber 74 via inlet ports 82 and 84. Coolant is fed to the resonancemodule 74 by a coolant pump 86 which is fluidly connected to inlet ports82, 84 via external fluid lines 88 and 90. To assist in maintaining thedesired coolant temperature, coolant lines 88 and 90 are sufficientlyinsulated to limit any variance in coolant temperature as it enters thevacuum pumped resonance module 74 and avoid condensation in non-vacuousareas. Although two inlet and outlet ports for the coolant are shown inFIG. 2, in other embodiments, there may be just one, since the coolingtubes 76 are circular around the imaging volume 72, or there may be morethan two to provide more consistent flow circulation.

[0032] Coolant pump 86 circulates coolant at a temperature dependent onsystem needs and, in accordance with the present invention, at a coolanttemperature independent of the dew point temperature of the ambient. Byremoving any moisture in the vacuum enclosure 74, the coolant may beinput through ports 82 and 84 at any desired temperature. That is, thecondensation effects resulting from the relationship between coolanttemperature and the ambient temperature are negated by the evacuation ofmoisture from the vacuum enclosure 74 by the vacuum pump 78 and anappropriate control 80.

[0033] Coolant entering the resonance module 74 travels through coolingtubes 76 and while doing so absorbs heat from the coils. The coolantcarrying the heat entrained therein away from the gradient coils exitsthe vacuous resonance module 74 through outlet ports 92 and 94 whichtransports the heated coolant to a chiller/heat exchanger 96 via returnlines 98, 100. Chiller 96 is configured to dissipate heat absorbed inthe coolant using a heat exchanger and a compressor (not shown) in aknown technique and lower the coolant temperature to a desiredtemperature dictated by the computer/control 80.

[0034] Operation of chiller 96 is controlled by computer/control 80 todrive the temperature of the liquid coolant to a desired value.Regulation of the coolant temperature in accordance with the presentinvention allows for dynamic adjusting of the coolant temperature tokeep the patient surface and other resonance module temperatures, suchas, the warm bore surface temperature adjacent to the resonance module,within specified limits. That is, if the heat dissipation requirementsincrease, the temperature of the coolant may be decreased below the dewpoint temperature if necessary. Further, if the heat or powerdissipation needs are reduced, the temperature of the coolant may beallowed to increase thereby decreasing the amount of energy exerted bythe chiller 96. As a result, down times of the MRI apparatus 10 to allowthe system to cool are avoided, and further, the MRI apparatus 10 may beimplemented with applications and imaging sequences requiring higherpower input to the gradient coils. A method to regulate the coolanttemperature will be discussed with particular reference to FIG. 3.

[0035] Still referring to FIG. 2, a number of operation sensors areprovided to monitor the temperature, pressure, and relative humidity ofthe vacuum enclosure 74 and various surfaces of the MR apparatus 10.Temperature sensors 102 are placed to measure the temperature of theresonance module 74, the patient surface 75 and the warm bore surface77. Further, pressure and relative humidity sensors 104, 106 arepositioned within the resonance module 74 to measure the vacuum pressureand condensation properties within the resonance module 74. The sensedrelative humidity and pressure are transmitted to the computer/control80 which in turn transmits control signals to vacuum pump 78 to increaseor decrease the pressure in the resonance module 74. Temperature sensors102 transmit temperature data of the resonance module 74, patient boresurface 75, and the warm bore surface 77. In response to the receivedtemperature signals, computer 80 transmits control signals to chiller96. As the temperature of the bore surfaces and the resonance module 74increase, the computer/control 80 transmits instructions to the chiller96 to adjust the temperature of the liquid coolant flowing to theresonance modules 74. Alternatively or in conjunction with temperatureadjustment, as the need to dissipate heat from the gradient coilschanges, the computer/control 80 may also adjust the flow rate ofcoolant pump 86 to increase or decrease temperatures in the MR device 10to a desired temperature. Furthermore, the temperature, pressure, andrelative humidity sensors 102, 104, 106 may also be implemented totrigger the computer/control 80 to disable the gradient coil drivers ifan anomalous condition is detected.

[0036] Referring to FIG. 3, an algorithm 110 is provided to dynamicallyregulate coolant temperature for dissipating heat generated byexcitation of the gradient coil assembly. Algorithm 110 begins at 112with reading the pressure within the resonance module 114 and thehumidity 116, and if either the pressure sensor or the humidity sensorindicates a loss of pressure or a certain level of humidity within theresonance module 118, 120, power to the gradient coils is limited andthe system is shut down and sends a warning to the operator 122, atwhich time the system is capable of looping back to the beginning of thecontrol 112 and continually monitoring the pressure and humidity. Ifthere is no humidity present, nor a pressure loss, 118, 124 activecontrol of coolant temperatures is enabled 126, which includes readingtemperature signals from the temperature sensors on the patient surface128, in the resonance module 130, and on the warm bore surface 132. Ifall the temperatures are within set limits 134, 136, no action isrequired 138 and the control algorithm loops back to the beginning 112and continues as previously described. However, if the temperatures arenot within the set limits 134, 140, the coolant temperature is adjusted142 as dictated by the temperatures sensed at the patient surface, inthe resonance module, and on the warm bore surface. Alternatively, or inconjunction therewith, the flow rate of the coolant can also be adjusted142. After the adjustment of the coolant and/or the flow rate 142, thesystem loops back to the beginning of the algorithm 112 and continuallyrepeats the aforementioned sequence of instructions.

[0037] Once the new coolant inlet temperature and/or flow rate isdetermined, the coolant temperature is adjusted by the chiller or heatexchanger 96, FIG. 2, and/or the coolant flow rate is adjusted by thecoolant pump 86, FIG. 2. Although the coolant temperature and/or flowrate have been adjusted to maintain a maximum and minimum temperaturewithin a specified range, the control process of the present inventionis configured to continually monitor the temperatures so that furtheradjustments to the coolant temperature and/or flow rate may be made tomaintain the temperature range within specified requirements. After thescanning is complete the coolant inlet flow rate and coolanttemperatures can be reset to default values.

[0038] The present invention includes a system for cooling electricalcoils that includes a cooling tube assembly for transferring heat fromat least one electrical coil via a coolant traveling through the coolingtube assembly. A heat exchanger is further provided for receiving thecoolant from the cooling tube assembly and removing heat therefrom. Thesystem also includes an enclosure having a cooling assembly therein andhaving an internal dew point less than that of a surrounding atmosphere.A control system receives feedback indicative of operating conditions ofthe electrical coil and in response thereto, provides signals to theheat exchanger to dynamically adjust coolant temperature.

[0039] In a further embodiment of the present invention, a coolingsystem for an MRI device includes a set of coolant tubes in thermalcontact with a set of gradient coils of the MRI device and having acoolant pass therethrough. A heat exchanger is connected to the set ofcoolant tubes to remove heat from the coolant and a vacuum chamberenclosing the set of coolant tubes. The system also includes at leastone temperature sensor in thermal contact to sense temperature of the MRdevice and a humidity sensor positioned to sense humidity in the vacuumchamber. A controller is connected to receive temperature indicativesignals from the temperature sensor and control coolant temperature inresponse thereto.

[0040] In yet a further embodiment of the present invention, an MRIapparatus is provided and includes a magnetic resonance imaging systemhaving a plurality of gradient coils positioned about a bore of a magnetto impress a polarizing magnetic field. The magnetic resonance imagingsystem further includes an RF transceiver system and an RF switchcontrolled by a pulse module to transmit RF signals to an RF coilassembly to acquire MR images. The MRI apparatus also includes a coolingsystem having a temperature sensor positioned to sense an indicationgradient coil temperatures, a set of coolant tubes having a coolant passtherethrough and in thermal contact with the gradient coils of the MRIsystem, and a heat exchanger connected to the coolant tubes to removeheat from the coolant. A vacuum chamber encloses the coolant tubes andhas a vacuum pump connected thereto. At least one pressure sensor isprovided and connected to sense pressure within the vacuum chamber. TheMRI apparatus further includes a control connected to receive signalsfrom the pressure sensor and send signals to the vacuum pump to controland maintain a vacuum within the vacuum chamber. The control is alsoconnected to receive signals from the temperature sensor and control thecoolant temperature in response, thereby maintaining a steadytemperature in and around the resonance module.

[0041] In a further embodiment of the present invention, a method ofcooling an MRI includes the step of creating a sealed enclosure about aset of gradient coils. The method further includes the steps of removingmoisture from the sealed enclosure and recirculating a coolant through aseries of cooling tubes in the sealed enclosure and through a heatexchanger. Next, a representation of gradient coil temperature ismonitored during MRI operation. Further, the method includes the step ofadjusting the temperature of the coolant in response to therepresentation of gradient coil temperature.

[0042] The present invention is particularly adaptable to retrofittingexisting MR scanners, and accordingly includes a coolant control systemkit adaptable to an MR device that includes a humidity sensor positionedto sense humidity in a resonance module and at least one temperaturesensor in thermal contact to sense temperature of a portion of the MRdevice. The kit also includes a controller connected to receivetemperature indicative signals from the temperature sensor and controlcoolant temperature in response thereto.

[0043] The present invention has been described in terms of thepreferred embodiment, and it is recognized that equivalents,alternatives, and modifications, aside from those expressly stated, arepossible and within the scope of the appending claims.

1. A cooling system comprising: a cooling tube assembly for transferringheat from at least one electrical coil via a coolant traveling throughthe cooling tube assembly; a heat exchanger for receiving the coolantfrom the cooling tube assembly and removing heat therefrom, the heatexchanger having a chiller to drive the coolant to a desiredtemperature; an enclosure having the cooling tube assembly therein andhaving an internal dew point less than that of a surrounding atmosphere;and a control system that receives feedback indicative of operatingconditions of the electrical coil and in response thereto, providescontrol signals to the chiller to dynamically adjust coolanttemperature.
 2. The cooling system of claim 1 further comprising ahumidity removal device connected to the enclosure for removing humiditytherefrom and maintaining the enclosure under a negative pressure. 3.The cooling system of claim 2 incorporated into an MRI scanner tocontrol temperatures within a resonance module, on a patient boresurface, and on a warm bore surface adjacent to a magnet enclosure. 4.The cooling system of claim 2 wherein the humidity removal deviceincludes: a vacuum pump for removing humidity from the enclosure; apressure sensor for monitoring internal pressure in the enclosure; and acontrol for monitoring the internal pressure in the enclosure andcontrolling the vacuum pump in response thereto.
 5. The cooling systemof claim 1 wherein the control system further comprises: a temperaturesensor to sense temperature of the electrical coil; a humidity sensor tosense humidity within the enclosure; and a computer to control theinternal dew point in the enclosure in response to the humidity sensedand to control the electrical coil temperature in response to the sensedelectrical coil temperature.
 6. The cooling system of claim 5 whereinthe computer controls the electrical coil temperature by dynamicallyadjusting the coolant temperature out of the chiller to maintain arelatively constant electrical coil temperature.
 7. The cooling systemof claim 4 further comprising a feedback control loop for maintaining asteady electrical coil temperature by dynamically adjusting coolanttemperature through the cooling tube assembly in response to electricalcoil temperature, and when the electrical coil temperature exceeds agiven temperature, adjusting the coolant temperature below an ambientdew point temperature if necessary.
 8. The cooling system of claim 1further comprising a coolant pump connected to and controlled by thecontrol system to adjust a flow rate in response to the feedback to thecontrol system.
 9. The cooling system of claim 3 wherein the controlsystem is connected to sound an alarm or display a warning message anddisable the electrical coils in response to an anomalous condition. 10.A cooling system for an MRI device comprising: a set of coolant tubes inthermal contact with a set of gradient coils of the MR device and havinga coolant pass therethrough; a heat exchanger connected to the set ofcoolant tubes to remove heat from the coolant; a vacuum chamberenclosing the set of coolant tubes; at least one temperature sensor inthermal contact to sense temperature of the MR device; and a controllerconnected to receive temperature indicative signals from the temperaturesensor and control coolant temperature in response thereto.
 11. Thecooling system of claim 10 further comprising: a humidity sensorpositioned to sense humidity in the vacuum chamber; and wherein thecontroller is connected to receive humidity indicative signals and limitpower to the MRI device if the humidity in the vacuum chamber exceeds adew point level.
 12. The cooling system of claim 10 further comprising:a vacuum pump connected to the vacuum chamber; at least one pressuresensor connected to sense pressure within the vacuum chamber; andwherein the controller is connected to receive indicative pressuresignals from the pressure sensor and in response thereto, control avacuum pump to maintain a vacuum within the vacuum chamber.
 13. Thecooling system of claim 10 further comprising a coolant flow controlvalve connected to receive control signals from the controller andadjust coolant flow to the cooling system.
 14. The cooling system ofclaim 10 having a first temperature sensor in thermal contact with apatient bore surface of the MRI device, a second temperature sensor inthermal contact with a resonance module, and a third temperature sensorin thermal contact with an outer bore surface, each temperature sensorconnected to transmit temperature indicative signals to the controllersuch that the controller maintains temperatures for each sensor.
 15. Thecooling system of claim 10 further comprising a feedback loop to lowercoolant temperature in response to an increase in gradient coiltemperature.
 16. The cooling system of claim 15 wherein the feedbackloop and the temperature controller maintain the gradient coiltemperature constant regardless of variations in power to the gradientcoils.
 17. An MRI apparatus comprising: a magnetic resonance imaging(MRI) system having a plurality of gradient coils positioned about abore of a magnet to impress a polarizing magnetic field and an RFtransceiver system and an RF switch controlled by a pulse module totransmit RF signals to an RF coil assembly to acquire MR images; and acooling system having: a temperature sensor positioned to sense anindication of gradient coil temperature; a set of coolant tubes having acoolant pass therethrough and in thermal contact with the gradient coilsof the MR system; a heat exchanger connected to the coolant tubes toremove heat from the coolant; a vacuum chamber enclosing the coolanttubes; a vacuum pump connected to the vacuum chamber; at least onepressure sensor connected to sense pressure within the vacuum chamber;and a control connected to receive signals from the pressure sensor andsend signals to the vacuum pump to control and maintain a vacuum withinthe vacuum chamber, and connected to receive signals from thetemperature sensor and control a coolant temperature in response,thereby maintaining a steady gradient coil temperature in and around thevacuum chamber.
 18. The MRI apparatus of claim 17 further comprising: aset of coolant supply/return lines having thermal insulation thereoverand connecting the heat exchanger to the set of coolant tubes; ahumidity sensor positioned to sense humidity in the vacuum chamber andconnected to the control, the control programmed to limit power to thegradient coils if the sensed humidity in the vacuum chamber exceeds adew point.
 19. The MRI apparatus of claim 17 further comprising a firsttemperature sensor in thermal contact with a patient bore surface of theMRI system, a second temperature sensor in thermal contact with aresonance module, and a third temperature sensor in thermal contact withan outer bore surface.
 20. The MRI apparatus of claim 17 furthercomprising a coolant flow control valve connected to receive controlsignals from the control to adjust coolant flow control to the coolantsystem.
 21. A method of cooling an MRI comprising the steps of: creatinga sealed enclosure about a set of gradient coils; removing moisture fromthe sealed enclosure; recirculating a coolant through a series ofcooling tubes in the sealed enclosure and through a heat exchanger;monitoring an indication of gradient coil temperature during MRoperation; and adjusting a temperature of the coolant in response to theindication of gradient coil temperature.
 22. The method of claim 21further comprising the steps of: providing the indication of gradientcoil temperature feedback in real-time; and lowering coolant temperaturebelow an ambient dew point if necessary to allow higher power levels tothe gradient coils.
 23. The method of claim 22 further comprising thesteps of: monitoring a humidity level in the sealed enclosure; andlimiting power to the gradient coils if the coolant level needed wouldcreate condensation in the sealed enclosure based on the humidity levelmonitored.
 24. The method of claim 21 wherein the step of removingmoisture is performed by creating a vacuum in the sealed enclosure. 25.A coolant control system kit adaptable to an MR device comprising: ahumidity sensor positioned to sense humidity in a resonance module; atleast one temperature sensor in thermal contact to sense temperature ofa portion MR device; and a controller connected to receive temperatureindicative signals from the temperature sensor and control coolanttemperature in response thereto.
 26. The coolant control system kit ofclaim 25 wherein the at least one temperature sensor includes a firsttemperature sensor in thermal contact with a patient bore surface of theMRI device, a second temperature sensor in thermal contact with aresonance module, and a third temperature sensor in thermal contact withan outer bore surface, each temperature sensor connected to transmittemperature indicative signals to the controller such that thecontroller maintains temperatures for each sensor within a given range.27. The coolant control system kit of claim 25 wherein a humidity sensoris positioned to sense humidity in the vacuum chamber, and wherein thecontroller is connected to receive humidity indicative signals and limitpower to the MRI device if the humidity in the vacuum chamber exceeds adew point level.
 28. An MR cooling system comprising: means fortransferring heat from at least one electrical coil via a coolanttraveling therethrough; means for receiving the coolant from the meansfor transferring heat and removing therefrom; an enclosure having themeans for transferring heat therein and having an internal dew pointless than that of a surrounding atmosphere; and a control means forreceiving feedback indicative of operating conditions of the electricalcoil and in response thereto, dynamically adjusting coolant temperature.29. The MR cooling system of claim 28 further comprising: a means forremoving humidity from the enclosure; a pressure sensor means formonitoring internal pressure in the enclosure; and a control means formonitoring the internal pressure in the enclosure and controlling themeans for removing humidity in response thereto.
 30. The MR coolingsystem of claim 28 further comprising: a means for sensing temperatureof the electrical coil; a means for sensing humidity within theenclosure; and a means for controlling the internal dew point in theenclosure in response to the humidity sensed and for controlling theelectrical coil temperature in response to the sensed electrical coiltemperature.